No difference between doses in skin anesthesia after lidocaine delivered via iontophoresis.

CONTEXT

Iontophoresis is a method of administering medications transcutaneously using galvanic current. Dose is the product of current amplitude and treatment duration. It is assumed that higher doses of iontophoresis are more effective in delivering medication, yet research supporting this claim is insufficient.

OBJECTIVE

To compare high-dose lidocaine iontophoresis (80 mA-min), standard-dose lidocaine iontophoresis (40 mA-min), and 2 sham treatments indirectly by measuring skin anesthesia.

DESIGN

Double-blind crossover study.

SETTING

Research laboratory.

PARTICIPANTS

15 healthy volunteers (10 women, 5 men: age 24.06 ± 2 y, height 169.7 ± 8.3 cm, weight 72.5 ± 14.2 kg).

INTERVENTION

Four treatments were counterbalanced and applied on the anterior forearm: 2 true interventions (40 and 80 mA-min) and 2 sham interventions separated by at least 24 h. The true-intervention doses were applied at a current of 2 mA with 2.5 ml 2% lidocaine HCL for 20 and 40 min. The sham treatments were 2.5 ml of lidocaine without galvanic current (intensity = 0 mA, 40 min) and 2.5 ml of saline solution (galvanic current of 2 mA for 40 min).

MAIN OUTCOME MEASURES

Semmes-Weinstein monofilament scores were taken preintervention and postintervention (at 0, 20, 40, and 60 min) to measure skin anesthesia.

RESULTS

A significant interaction between treatment and time (F = 4.137, P < .01) was identified. The 40-mA-min dose produced greater anesthesia than the lidocaine and saline shams at all times. The 80-mA-min dose produced greater anesthesia than saline sham at all times. There was a significant difference noted, with 40 mA-min over 80 mA-min, at the 20-min posttest, but there were no other significant differences between the 40- and 80-mA-min doses at 0, 40, or 60 min posttreatment or between the 2 sham treatments at any time.

CONCLUSIONS

The 40-mA-min treatment was just as effective as the 80-mA-min treatment, suggesting that shorter treatments may be more time efficient for clinicians and patients.